The proposed study is designed to provide evidence for convergent validity, discriminant validity, predictive validity, sensitivity, and specificity fr the two-item underage drinking screening instrument designed by the National Institute on Alcohol Abuse and Alcoholism and the American Academy of Pediatrics. The study will use an accelerated longitudinal design with three cohorts (400 6th graders, 400 8th graders, and 400 10th graders). Each cohort will be assessed 7 times over a 31/2-year period, supporting longitudinal analyses across the 7-year period from 6th grade until the year after 12th grade. Participants will be sampled from public schools in Miami-Dade County, Florida, and the Maryland suburbs of Washington, DC. Students will be assessed in their classrooms twice per year. We will measure alcohol use, alcohol-related problems, alcohol use disorders, illicit drug use, sexual risk behavior, and externalizing problem behavior through well-validated self-report measures. We will also examine the extent to which the validity and effects of the screener vary according to the density of alcohol outlets within walking distance (a practical 1/4 mile radius) o each adolescent's home and school addresses, and according to Census-level poverty, affluence, residential stability, and family structure indices. Our analytic objectives will be to examine the extent to which scores on the screener items predict current and subsequent alcohol use, alcohol-related problems, diagnosable alcohol use disorders, illicit drug use, sexual risk behavior, and externalizing problem behavior - as well as to identify cutoff scores for the screener items that maximize the sensitivity and specificity of the instrument to identify adolescents at risk for alcohol problems. The present study will be the first to use the screener in a school setting, where the vast majority of adolescents can be accessed.